The Diagnosis and Management of Subclinical Hypothyroidism Is Assay-Dependent

Implications for Clinical Practice

Tejas Kalaria; Anna Sanders; Jonathan Fenn; Helen L. Ashby; Pervaz Mohammed; Harit N. Buch; Clare Ford; Rousseau Gama


Clin Endocrinol. 2021;94(6):1012-1016. 

In This Article


The laboratory using Abbott assays identified 40 samples from patients with SCH within 10 working days, by which time the laboratory using Roche assays had identified 53 samples from patients with SCH, thus 93 patient samples were included in the study.

The results of Roche and Abbott TSH assays (ρ 0.947, P < .001) and Roche and Abbott fT4 assays (ρ 0.921, P < .001) correlated, and their relationship was proportionate in nature for both TSH and fT4 assays (Figure 1). TSH and fT4 analysed using Roche assays were respectively 40% ± 15% and 16% ± 7% higher (P < .001) compared to Abbott assays.

Figure 1.

TSH (A) and fT4 (B) results analysed by Roche and Abbott assays on samples with subclinical hypothyroidism on at least one of the two analytical platforms (n = 93). URL and LRL are respectively upper and lower reference limits [Colour figure can be viewed at]

Of the 53 patients with SCH on the Roche assays (37 females, median age 65 years, IQR 49–78), 40 patients had normal thyroid function and 13 patients had SCH when analysed with the Abbott assays (Table 1). Of the 40 patients with SCH on the Abbott assays (34 females, median age 57 years, IQR 46–77), 28 patients had SCH, five patients had a raised TSH <10 mIU/L and low fT4, four patients had a TSH >10 mIU/L with normal fT4, and three patients had a TSH >10 mIU/L with a low fT4 when analysed on the Roche assay (Table 1). Based on their biochemistry results, therefore, 12 patients with SCH on the Abbott assays would be considered for levothyroxine replacement if their samples had been analysed using Roche assays.

Of the total 93 patients, 41 (44%) patients had SCH by both the methods. Of the rest 52 (56%) patients, 40 (43%) had normal thyroid function on Abbott assays, whereas 12 (13%) had biochemical indication for initiation of levothyroxine treatment on Roche assays, either TSH >10 mIU/L or fT4 below the lower reference range or both (Table 1).